Abstract: Pigments for inkjet inks are controllably functionalised to improve water-dispersibility, ozone resistance, etc., by irradiation of the pigment particle with high energy radiation, such as gamma radiation in air or by plasma activation, to form a stable functionalisable intermediate pigment particle, then activating the stable functionalisable intermediate, e.g. by heating, in the presence of a functionalising precursor (e.g. a polymer or polymerisable monomer) to form a modified pigment particle having one or more functionalising group grafted onto the pigment particle.